1. Field of the Invention
The present invention relates to a heat treatment apparatus for a substrate, such as a lamp annealer or a CVD device, for introducing gas into a furnace and applying a heat treatment on a substrate placed in the furnace for annealing, oxidation, nitridation, or film growth thereon. Particularly, the present invention relates to improvement of a structure for discharging gas introduced in a heat treatment furnace.
2. Description of the Related Art
One type of an apparatus for applying a heat treatment on substrates one by one includes a heat treatment furnace of a flat configuration with an opening at one side surface. In this type of heat treatment apparatus, one substrate is loaded into the heat treatment furnace through the opening and then the opening is shut by a cover. Active or inert gas is introduced into the heat treatment furnace. Various heat treatment is applied on the substrate such as annealing, oxidation, nitridation, and film growth on the surface thereof.
In order to improve uniformity and repeatability of the quality of heat treatment and to further increase throughput in such a substrate heat treatment apparatus, gas introduced into the heat treatment furnace must form a uniform flow within the furnace and be smoothly discharged without stagnation. It is also necessary to suppress inflow of outside air into the heat treatment furnace when the opening of the furnace is opened when a substrate is loaded into or unloaded from the furnace.
FIG. 1 is a longitudinal sectional view of the structure of the main components of a lamp annealer as an example of such a related heat treatment apparatus of related art. Referring to FIG. 1, a lamp annealer includes a heat treatment furnace of a flat configuration with a rectangular plane, and an opening at one side face. The heat treatment furnace includes a furnace main body 10 formed of quartz glass, and an attach unit integrally formed with furnace main body 10 at the opening side thereof. Furnace main body 10 includes a heat treatment chamber 16 in which a substrate is accommodated.
A gas inlet 14 is provided in furnace main body 10 at a side surface opposite to the side face where the opening is formed. Gas is introduced into heat treatment chamber 16 in furnace main body 10 through gas inlet 14. A substrate W is loaded through the opening into heat treatment chamber 16 of furnace main body 10 one by one.
Referring to the right side of FIG. 1, attach unit 12 includes a fore chamber 18 in communication with heat treatment chamber 16. Attach unit 12 includes an opening 20 of fore chamber 18 formed at one side face thereof and a gas exhaust unit 1 in the proximity of opening 20.
Opening 20 of attach unit 12 can be shut or opened by a cover 22. At the inside side face of cover 22, a connection rod not shown is fixedly attached. This connection rod is further connected to a susceptor 24 supporting substrate W. An O-ring 30 for shielding is provided between cover 22 and a sidewall of attach unit 12, and between a sidewall of attach unit 12 and the side face in which an opening of furnace main body 10 is formed.
A plurality of heat lamps 26 are arranged outside furnace main body 10 so as to respectively face the top furnace wall and the bottom furnace wall of furnace main body 10. The heating lamps facing the top furnace wall and the heat lamps facing the bottom furnace wall are arranged at right angles to each other.
Gas inlet 14 includes a gas supply port 28. Gas supply port 28 is connected to a gas supply unit including a mass flow controller or a switching valve via a piping not shown. Such a gas supply unit selectively provides active or inert gas such as oxygen, ammonia, nitrogen, argon, and nitrogen monoxide via the piping.
FIG. 2 is a plan transverse sectional view of an end portion of attach unit 12 of the lamp annealer of FIG. 1, and FIG. 3 shows an end view thereof taken along lines III--III of FIG. 2.
Referring to FIGS. 2 and 3, a lamp annealer of the related art includes a plurality of exhaust ports formed at the inner wall along the direction of the width of the heat treatment furnace at equal intervals. The gas introduced into heat treatment chamber 16 of the heat treatment furnace through gas inlet 14 flows along the surface of substrate W placed in heat treatment chamber 16 into fore chamber 18 from heat treatment chamber 16. The gas flow in fore chamber 18 is discharged via a plurality of exhaust ports 2 provided along the entire width of the heat treatment furnace at equal intervals.
In the above-described lamp annealer, gas is continuously discharged via gas exhaust unit 1 when a substrate is loaded into heat treatment chamber 16 via opening 20 of fore chamber 18 and also when unloaded from heat treatment chamber 16. The reason is set forth in the following.
In an apparatus that processes a semiconductor wafer having a diameter of 8 inches, for example, as substrate W, gas is introduced into heat treatment chamber 16 via gas inlet 14 at the rate of approximately 3 to 10 l/min. during heat treatment of substrate W with opening 20 of the heat treatment furnace shut. Opening 20 is opened when substrate W is loaded or unloaded into or from heat treatment chamber 16. Here, purge gas of nitrogen gas or the like is introduced via gas inlet 14 into heat treatment chamber 16 at the rate of approximately 20 to 40 l/min. in order to completely discharge gas from heat treatment chamber 16 used for heat treatment and to prevent introduction of outside air into heat treatment chamber 16 via opening 20.
In order to provide a uniform gas flow and reliably discharge the gas used for heat treatment, an approach can be considered where the discharge from gas exhaust unit 1 is inhibited and the used gas is discharged together with the purge gas through opening 20. However, there is problem according to the current reliability of the valve inserted in the piping connected to gas exhaust unit 1 to inhibit this discharge. There is a possibility of increase in the pressure in the heat treatment chamber 16 depending upon the operating time of the valve when opening 20 is shut by cover 22 after a substrate to be subjected to heat treatment is loaded into heat treatment chamber 16. The operator will be subjected to danger when the gas used for heat treatment is hazardous gas. Therefore, gas is continuously discharged via gas discharge unit 1 when substrate W is loaded or unloaded into or from heat treatment chamber 16 via opening 20.
Referring to FIGS. 4 and 5, it is assumed that the gas flow into fore chamber 18 from heat treatment chamber 16 is drawn and discharged via exhaust port 2 while opening 20 is open. In this case, a local rapid flow of gas occurs at the periphery of each exhaust port 2, and a current flow towards the interior of heat treatment chamber 16 is generated. As a result, there is a possibility of ingress of outside air 5 into heat treatment chamber 16 via the spacing between adjacent exhaust ports 2 as shown in FIG. 5. Outside air 5 may reach considerably into the interior of heat treatment chamber 16 due to convection caused by heat in heat treatment chamber 16.
Under such conditions, there is possibility of the atmosphere component remaining within heat treatment chamber 16 even after opening 20 is shut by cover 22 when substrate W is loaded therein. Such a component will adversely affect the subsequent heat treatment of substrate W.
The interior of heat treatment chamber 16 can be purged with inert gas for a relatively long time period prior to heat treatment to completely discharge the atmosphere component from heat treatment chamber 16. However, a long time will be required before a heat treatment is initiated, so that the throughput of the heat treatment is degraded. Furthermore, the running cost of the device may be increased due to increase of the consumed amount of gas.
When exhaust is carried out via exhaust port 2 provided at the inner wall of attach unit 12 during a heat treatment, a stagnation portion 4 of gas flow is generated at the cavity between exhaust port 2 and cover 22 as shown in FIGS. 1-3. When the type of gas introduced is to be exchanged, the gas within heat treatment chamber 16 cannot be replaced smoothly. The gas exchange operation is time consuming to degrade the throughput of the apparatus.